1. Field of the Invention
The present invention relates to a ribbon cable for use in electrical equipment such as telephones, electrostatic copying machines, microcomputers, printers, electronic calculators, video tape recorders, electronic ranges, various kinds of electric instruments mounted on a vehicle or the like.
2. Background
A typical conventional ribbon cable is shown in FIG. 4. As illustrated, the cable includes a plurality of metallic wires A, each made of soft copper, hard copper, beryllium copper or a similar copper alloy and having a rectangular crosssectional shape, and a sheathed layer b molded of an electrically insulating material such as rubber, synthetic resin or the like and having a relatively large width and a small thickness, with the metallic wires a sandwiched therebetween.
However, each metallic conductor is relatively heavy and corrodes easily in certain environments. Therefore, it has been proposed to make the conductors out of an electrically conductive composite material which is light weight and noncorrosive. The proposed composite material includes a thermoplastic resin as a matrix to which is added a carbon black, graphite powder and graphite fiber. Such an arrangement is disclosed in Japanese Patent Unexamined Publication No. SHO. 60-184,534. However, it has been found that the proposed composite material is disadvantageous in that it has a resistivity of approximately 10.sup.-2 .OMEGA..multidot.cm, resulting in insufficient electrical conductivity.
Since a thermoplastic synthetic resin is employed as the matrix of the ribbon cable, when the above electrically conductive composite material is used as the conductor, it has been discovered that the synthetic resin deforms due to the high temperature experienced under normal conditions. On the other hand, when a thermoplastic synthetic resin having a higher resistance to deformation at elevated temperatures is used as a raw material for the electric conductive composite material, it exhibits poor flexibility. Thus, the conventional ribbon cable does not exhibit properties required for use as a conductor.
The use of exfoliated graphite produced by oxidizing and baking graphite has been considered as an electrically conductive material which is light weight and non-corrosive, as disclosed in Japanese Patent Examined Publication No. Hei. 2-12,903.Exfoliated graphite has usually been used as a packing incorporated in a shaft shielding portion of a hydraulic machine or hydraulic equipment such as a valve, a pump or the like but it could not be practically used as a material for a conductor because of its very low mechanical strength.